A Study of Strain and Electric Field Induced Photocatalytic Crossover in g-C3N4/CoN4 Nanocomposite through DFT : Upgradation from Type-I to Type-II Photocatalyst for Water Splitting Reaction

Van der Waals (vdW) heterojunctions, consisting of two-dimensional monolayers, represent a recent category of materials characterized by their highly adjustable band alignment, bandgap energy, and bandgap transition characteristics. In this investigation, we employed density functional theory calculations to explore the formation of a vdW heterojunction involving heptazine-based graphitic carbon nitride (g-C3N4) monolayer and CoN4 (111) slab, denoted as g-C3N4/CoN4. This specific heterojunction holds promise as a potential catalyst for solar-driven photocatalysis in the water-splitting reaction. Upon the creation of the heterojunction, a type-I direct bandgap (Eg = 2.00 eV) is established, featuring appropriate conduction band minimum and valence band maximum levels in relation to the oxidation/reduction potentials for the water-splitting reaction. Moreover, the band alignment, bandgap energy, and transition type of the heterojunction can be tuned finely by applying external perpendicular electric fields (±0.5 V/Å) and biaxial strains of (±6 %). Notably, a -2% strain induces a type-II band alignment (Eg = 2.1 eV, direct), while an electric field of +0.5 V/Å also results in a type-II heterostructure (Eg = 1.90 eV, direct). The state-of-the-art DFT study reveals a photocatalytic crossover in g-C3N4/CoN4 from type-I to type-II in presence of bilateral strain and electric field.